The immediate and continuing aim of this line of investigation involves the development of strategies to probe the development and differentiation of phenotypic properties expressed by functionally distinct types of nerve, endocrine and immune cells, especially those involved in signal transduction mechanisms. The strategies in development include dual-laser fluorescence- activated cell analysis an sorting (FACS), light-microscopic characterization of cells in monolayer culture using immunoreagents reacting with detectable fluorescence signals emanating from cells in monolayer culture. Principal observations this year include: 1) further refinement of a voltage-sensitive indicator dye protocol for assaying membrane potential distributions in heterogeneous suspensions of embryonic and early postnatal cells from the mammalian CNS; 2) discovery of the development of functional GABA receptors coupled to K+ conductance mechanisms before the appearance of GABA receptors coupled to Cl- conductances; 3) discovery of the developmental time course of voltage-gated Na+ conductance, which occurs following the appearance of functional GABA receptors; 4) discovery of the expression of excitatory amino acid receptor functions developing after the appearance of voltage- gated Na+ conductances; 5) localization of the functional excitatory aminoacid receptors to the ventral region of the developing spinal cord; 6) FACS analyses of cell-cycle dynamics in co-transfected (CV-1) monkey kidney cells; 7) computer-assisted analysis of Ca2+ indicator dye signals emanating from FACS- sorted growth hormone and prolactin cells; 8) biochemical and autoradiographic dissection of MPTP dynamics in cultured astrocytes and catecholamine neurons; 9) development of a quinacrine staining protocol for use with FACS and light microscopic analysis of secretory activity; 10) FACS isolation of 0-2A glial progenitors.